The present invention relates to a sensor. More particularly, the invention relates to an end sensor for detecting the end of a thin film stuck to a base plate.
A printed circuit board, which is used in electronic equipment such as a computer, includes an electrically insulating base plate and a wiring pattern made of copper or the like formed on one or both sides of the base plate.
The printed circuit board is manufactured with a process as follows: A stacked assembly of a photosensitive resin (photoresist) layer and a light-transmissible resin film (protective film) for protecting the photosensitive resin layer is laminated by heat and pressure on an electroconductive layer formed on the electrically insulating base plate. A wiring pattern film is then overlaid on the stacked assembly. The photosensitive resin layer is exposed to light through the wiring pattern film and the light-transmissible resin film for a prescribed time period. The light-transmissible resin film is then peeled off. Afterwards, the exposed photosensitive resin layer is developed to form an etching mask pattern. The unnecessary portion of the electroconductive layer is then removed by etching. The remaining photosensitive resin layer is thereafter removed to complete the printed circuit board having the prescribed wiring pattern.
In the manufacturing process for the printed circuit board, a step of peeling off the light-transmissible resin film is required before the exposed photosensitive resin layer can be developed. Since, conventionally the light-transmissible resin film has been peeled off manually and the thickness of the film is small, the operator must be highly skilled and careful in order to avoid damaging or destroying the photosensitive resin layer due to peeling stress concentration or the like. For that reason, it is time-consuming to peel off the light-transmissible resin film. Therefore, the total work time for the manufacturing process is long.
In order to solve the problem, automatic thin film peeling device has been proposed in commonly assigned Japanese Patent Application No. 23179/86. In the automatic thin film peeling device, the end of a light-transmissible resin film included in a stacked assembly stuck to an electroconductive layer on an electrically insulating base plate is pull-raised (simultaneously pulled and raised) or separated by a needle-like projection pusher, and a fluid is blown against the pull-raised part of the film to automatically peel off the film. The end of the stacked assembly must be pull-raised to a height in a narrow range of about several millimeters in order to avoid damaging the photosensitive resin layer in an area provided with a wiring pattern. For that purpose, the end of the stacked assembly is detected by an end sensor (contact sensor) of an electrostatic capacity type or electrical resistance type s as to bring the projection pusher into exact contact with the surface of the electroconductive layer at the end of the stacked assembly to pull-raise the end of the light-transmissible resin film. The end sensor has a rod-like electroconductive contact member whose tip is oriented in a direction at an obtuse angle to the direction of conveyance of the electrically insulating base plate. The contact member is brought into contact with the surface of the electroconductive layer on the electrically insulating base plate and the surface of the light-transmissible resin film.
The detection of the end of the stacked assembly by the end sensor will now be described. The electrically insulating base plate bearing the stacked assembly stuck to the electroconductive layer is conveyed toward a light-transmissible resin film peeling position. When the downstream end (in the direction of conveyeance of the electrically insulating base plate) of the stacked assembly has passed by the tip (which is separated from the conveyance passage for the base plate) of the electroconductive contact member of the end sensor by a prescribed length, the conveyance of the electrically insulating base plate is stopped. The tip of the electroconductive contact member is then brought into contact with the surface of the light-transmissible resin film of the stacked assembly. Subsequently, the electrically insulating base plate is moved back in the direction opposite to that of its conveyance. When the electroconductive contact member of the end sensor has reached the end of the stacked assembly, contact of the tip of the contact member with the surface of the light-transmissible resin film is replaced by that of the tip of the contact member with the surface of the electroconductive layer on the base plate. At that time, the electrostatic capacity of the end sensor (if it is of the electrostatic capacity type) or the electrical resistance of the end sensor (if it is of the electric resistance type) changes and the end of the stacked assembly is detected in terms of the change.
However, since the tip of the electroconductive contact member of the above-mentioned end sensor is oriented in a direction at an obtuse angle to the direction of the conveyance of the electrically insulating base plate, the base plate must be moved back in order to detect the end of the stacked assembly. For that reason, there is a problem in that the time which it takes for the end sensor to detect the end of the stacked assembly is long.
Moreover, the tip of the electroconductive contact member of the end sensor has a tendency to catch the conveyed electrically insulating base plate, particularly if the base plate is so thin as to sag during conveyance or is warped or deformed for some reason. Thus, there is another problem in that the electroconductive contact member is likely to be damaged or destroyed.
Since the time which it takes for the end sensor to detect the end of the stacked assembly is long, the number of light-transmissible resin films which can be peeled off per unit time is small. For that reason, there is still another problem in that the productivity of the automatic thin film peeling device having the end sensor is low.